Protein folding studies are directed towards the goal of achieving the capability of designing novel polypeptide sequences which will fold into desired shapes with medically useful activities. A potentially useful class of snythetic proteins would be small inhibitors of enzymes. Many natural inhibitors consist of globules with a protruding amino acid which resembles the enzyme's substrate, such that the inhibitor competes for enzyme active sites in binding reactions. Enzyme inhibitors regulate many physiological processes such as complement fixation, blood-clotting, ovum fertilization, and cell-cell surface interactions. The objective of the proposed research is to develop strategies for directing formation of specific disulfides in a solution containing many different cysteines. The proposed research will study disulfide pairing beteween cysteine-containing fragments obtained from inexpensive commercially available proteins or synthesized directly in the labortory. Success would suggest synthetic sequences containing portions of the same peptides in a single chain, yielding the same specific pairing with a resultant specific topology. Different sequences could be designed for producing a collection of novel mainframes. These would serve as the basis for subsequent inhibitor production by addition of protruding amino acids at different locations on the main-frame. This proposal will test the hypothesis that the formation of specific bridges can be controlled by choosing appropriate positions for the cysteines in the polypeptide sequence and by surrounding the cysteines with appropriate positive, negative, or beta-branched residues. Experiments will measure quantitative effects of such factor on the microscopic rate constants in disulfide exchange reactions. These rates will be used to suggest peptide mixtures where particular disulfides are predicted to predominate at equilibrium. The predictions will be evaluated experimentally by establishing disulfide interchange equilibria between peptides, separating the products and determining their relative concentrations.